Hot-Stamped Closed-Section Frame Member for Bending Energy Absorption
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Solution Overview
Problem
Existing frame members used in vehicles face challenges in achieving both weight reduction and high energy absorption efficiency, particularly when subjected to bending loads during collisions.
Innovation Solution
A frame member is designed with a closed cross-sectional shape featuring flat parts and a recessed bead part, where the wall portions of the bead have a specific radius of curvature, Vickers hardness, and a controlled standard deviation ratio of hardness frequency distribution, optimizing the width of the wall portion relative to the effective width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the member thickness is reduced to achieve weight reduction, then the weight decreases, but the energy absorption efficiency and structural stability deteriorate
Solution Approach 1:
The frame member cross-section is segmented into multiple functional zones: flat parts for overall structural stability, recessed bead parts for localized reinforcement, and wall portions with specific geometric features. This segmentation allows each zone to contribute differently to weight reduction and energy absorption, enabling thin-walled construction while maintaining high energy absorption efficiency through optimized stress distribution in each segment.
Solution Approach 2:
The recessed bead parts introduce local geometric features with specific radii of curvature (50 mm or greater) and controlled dimensions (width 0.5-2.5 times effective width). These local quality modifications create zones of enhanced ductility and energy absorption capacity within the thin-walled structure, allowing the member to undergo controlled plastic deformation and absorb more energy per unit mass compared to uniform thin-walled sections.
2Strength
If the steel sheet strength is increased to improve proof stress, then the proof stress increases, but the material becomes more prone to brittle fracture and loses ductility
Solution Approach 1:
The recessed bead parts with large radii of curvature (≥50 mm) create local zones with different stress states compared to the flat parts. These localized geometric features promote gradual stress redistribution and plastic deformation initiation in controlled regions, preventing sudden brittle fracture propagation even in high-strength materials. The specific width ratio (0.5-2.5 times effective width) ensures optimal balance between local reinforcement and overall ductility.
Solution Approach 2:
The recessed bead parts incorporate curved surfaces with radii of curvature of 50 mm or greater, which fundamentally differ from the flat parts. These curved geometries distribute stress more uniformly and prevent stress concentration at sharp corners, thereby enhancing fracture resistance. The curvature allows high-strength materials to deform plastically in a controlled manner, maintaining reliability while utilizing the high proof stress capability of advanced steel sheets.
3Strength
If a recessed bead is added to suppress elastic buckling, then the proof stress improves, but the structural complexity and manufacturing difficulty increase
Solution Approach 1:
The cross-section is divided into simple flat parts and recessed bead parts, where each segment has a well-defined geometric role. The flat parts maintain overall structural simplicity, while the recessed bead parts provide targeted buckling suppression. This segmentation allows the complex function of buckling resistance to be achieved through localized features rather than complicating the entire cross-sectional geometry, facilitating manufacturing while improving proof stress.
Solution Approach 2:
Rather than making the entire cross-section complex, the invention introduces recessed bead parts with specific local geometric parameters (radius ≥50 mm, width 0.5-2.5 times effective width) at strategic locations. This local quality approach suppresses elastic buckling in critical regions while keeping the rest of the structure simple and manufacturable, balancing proof stress improvement with manufacturing feasibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively prevents bending fracture and suppresses elastic buckling, resulting in high energy absorption performance and efficiency, even when using high-strength thin materials.
Implementation Method 1
A frame member formed by hot-stamping a steel sheet
Data Source
Figure 1~2
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AI summary
Provided is a frame member formed by hot-stamping a steel sheet. The frame member has a closed cross section portion in which a cross section perpendicular to a longitudinal direction is a closed cross section, and the closed cross section portion has at least two flat parts having a radius of curvature larger than a maximum external dimension of the cross section, and a recessed bead part formed between the two flat parts. The recessed bead part has a pair of wall portions which have a radius of curvature of 50 mm or greater, and protrude toward an inside of the closed cross section portion from end portions of the two flat parts facing each other via a pair of bent portions bent toward an inside of the closed cross section. A Vickers hardness of a thickness middle portion in the wall portion is 520 Hv or greater, a width of the wall portion is 0.5 times or greater and 2.5 times or less an effective width We, and a standard deviation ratio obtained by dividing a standard deviation of hardness frequency distribution in a surface layer portion in the wall portion by a standard deviation of hardness frequency distribution in the thickness middle portion in the wall portion is less than 1.0.